In general, a coated steel sheet is subjected to press working or bending in forming into, for example, a panel for a television and is required to exhibit bendability and good appearance after press working. In general, a precoated steel sheet (coated steel sheet) is formed from a double coated steel sheet, in which usually, a modified polyester resin or an epoxy resin is primarily used as an undercoating film on the external surface side, to ensure the adhesion to the base steel sheet, the corrosion resistance, and the like, and furthermore, a polyester based coating film, an acryl based coating film, or the like is used as an overcoating film on the external surface side, to provide mainly the stain resistance, the design flexibility, the scratching resistance, the ethanol resistance, the barrier performance which is the hydrochloric acid resistance or the alkali resistance, and the like. Moreover, a triple coated steel sheet, in which an intermediate coating film is disposed between the undercoating film and the overcoating film, is also mentioned.
As disclosed in Japanese Unexamined Patent Aplication Publication No. 4-215873, in general, a conventional double coated steel sheet is required to have a film thickness of undercoating film of about 5 μm and a film thickness of overcoating film of at least 12 μm, and the total film thickness of these coating films is specified to be 20 μm or more from the viewpoint of concealment performance and the like. However, to form 20 μm of thick coating film, times for coating and baking increase and a larger thickness of the coating is disadvantageous from the viewpoint of production cost. Consequently, thickness reduction of coating film has been desired from the viewpoint of rationalization of coating operation and savings in resources.
In response thereto, we proposed a coated steel sheet having coating film hardness excellent in bendability and appearance after press working even when the film thickness was 10 μm or less on the basis of addition of resin particles to a coating film in Japanese Unexamined Patent Application Publication No. 2007-269010.
According to the developments in JP '010, a coated steel sheet having a coating film thickness of the coated steel sheet of 10 μm or less was obtained.
Meanwhile, in recent years, as flat-panel televisions have become popular, the demand for coated steel sheets having colored, especially black, films have increased regarding, for example, a panel for a flat-panel television.
Then, we attempted production of a black-coated steel sheet through addition of a black pigment on the basis of JP '010. As a result, it became clear that there was room for improvement in appearance of black-coated steel sheets when particularly severe press working was performed.
It could therefore be helpful to provide a black-coated steel sheet exhibiting a good appearance after press working, as well as a worked material thereof, especially a panel for a flat-panel television.